Some embodiments relate to a gearing assembly, and in particular a gearing assembly configured to provide at least three ratios including 1:1 in a simplified and compact manner.
Assemblies according to some embodiments may be found useful in a variety of vehicular applications or in other machinery where a simple, robust and compact gearbox is required. Gearing assemblies are used commonly on vehicles where it is desired to drive a wheel or axle at a different rotational speed to the revolutions of an engine. Assemblies according to some embodiments may find particular application in a gearing system for an electrical hub drive, and applications of some embodiments are discussed herein in that context by way of example, although some embodiments are not limited to such applications.
Electric hub drives, or hub-mounted electric drive (HMED) units are finding increasing use on vehicles where it is advantageous for the wheels to be driven independently. Applications include for example large vehicles and, vehicles adapted for use on difficult and for example steep or uneven terrain. HMED units are finding increasing use on hybrid vehicles. HMED units are finding increasing use on military vehicles particularly for use on difficult terrain.
Each wheel is provided with a hub-mounted electric drive assembly typically including a housing containing an electric motor, and a drivetrain including a drive shaft, arranged inside a suitable hub-mounted housing. An output shaft of the hub drive drives the wheel. The hub drive assembly must fit within the space available inside the diameter and the overall width of the wheel rim and tyre assembly.
The use of individual hub-mounted electric drive units eliminate the need for conventional transmission and drive shafts and offers enhanced vehicle capabilities through improvements in vehicle performance, fuel economy, design configuration, increased stealth capability and reduced whole-life costs.
An electric hub drive needs to have large torque range and a large speed range, and should be compact. A multi-speed gear change mechanism is desirable to facilitate this. Higher gear ratios can be used to provide higher torques at lower speeds and lower gear ratios can be used to allow for higher speeds (with low available output torque).
A gearing assembly with two speeds including a 1:1 ratio and a planetary gear set reduction selectively engageable by mechanism of a simple and compact dog clutch arrangement is described in EP1692416. An adaptation of this mechanism to provide a third ratio for example by provision of a second planetary gear set in series with the first could significantly complicate the required dog clutch arrangement. For example a dog clutch for high gear selection may be provided inside a tubular shaft between the motor rotor and the sun gear of the mid stage with radial pins and slots for actuation.